Stable phase boundaries between the 7x7 and the 5x2 Au structures on a Si(111) surface studied by high-temperature STM

Phase boundaries between the 7x7 and the 5x2 Au structures on a Si(111) surface, which were located along the two-fold direction of the 5x2 structure, were dynamically studied using high-temperature scanning tunneling microscopy (STM) during Au deposition at 500 degrees C. Two types of stable phase boundaries were observed depending on the growth direction of the 5x2 domain. The stable phase boundaries had adatoms of the unfaulted half at the edge of the 7x7 side. The formation of an unstable phase boundary was quickly followed by the growth of new rows of the 5x2 structure next to the boundary which formed a stable phase boundary. These results suggest that the stacking fault of the 7x7 structure at a phase boundary is unstable.